如何:使用查询路径调整结果(实体框架)
本主题提供的示例介绍如何指定特定的查询路径,该查询路径用于定义在概念模型中对特定对象进行查询时会返回哪些相关对象。 本示例中的查询返回单个 Contact 对象及所有相关的 SalesOrderHeader 对象和 SalesOrderDetail 对象。
若要指定查询路径,请将对象图的字符串表示形式传递给 ObjectQuery 的 Include 方法。 可以在任何实体框架 查询上应用 Include 方法:LINQ to Entities 、Entity SQL 或查询生成器方法。
本主题中的示例基于 Adventure Works 销售模型。若要运行本主题中的代码,则必须已经将 Adventure Works 销售模型添加到了您的项目中,并且已经将项目配置为使用实体框架。有关更多信息,请参见如何:使用实体数据模型向导(实体框架)或如何:手动配置实体框架项目和如何:手动定义实体数据模型(实体框架)。
示例
下面的示例指定一个返回 Contact 与相关 SalesOrderHeader 和 SalesOrderDetail 对象的查询路径。
Using context As New AdventureWorksEntities()
' Define a LINQ query with a path that returns
' orders and items for a contact.
Dim contacts = (From contact In context.Contacts.Include("SalesOrderHeaders.SalesOrderDetails") _
Select contact).FirstOrDefault()
' Execute the query and display information for each item
' in the orders that belong to the contact.
For Each order As SalesOrderHeader In contacts.SalesOrderHeaders
Console.WriteLine(String.Format("PO Number: {0}", order.PurchaseOrderNumber))
Console.WriteLine(String.Format("Order Date: {0}", order.OrderDate.ToString()))
Console.WriteLine("Order items:")
For Each item As SalesOrderDetail In order.SalesOrderDetails
Console.WriteLine(String.Format("Product: {0} Quantity: {1}", _
item.ProductID.ToString(), item.OrderQty.ToString()))
Next
Next
End Using
using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
// Define a LINQ query with a path that returns
// orders and items for a contact.
var contacts = (from contact in context.Contacts
.Include("SalesOrderHeaders.SalesOrderDetails")
select contact).FirstOrDefault();
// Execute the query and display information for each item
// in the orders that belong to the contact.
foreach (SalesOrderHeader order in contacts
.SalesOrderHeaders)
{
Console.WriteLine(String.Format("PO Number: {0}",
order.PurchaseOrderNumber));
Console.WriteLine(String.Format("Order Date: {0}",
order.OrderDate.ToString()));
Console.WriteLine("Order items:");
foreach (SalesOrderDetail item in order.SalesOrderDetails)
{
Console.WriteLine(String.Format("Product: {0} "
+ "Quantity: {1}", item.ProductID.ToString(),
item.OrderQty.ToString()));
}
}
}
Include 方法返回查询对象,您可以对一个 ObjectQuery 多次调用此方法,从而包括来自多个关系的实体,如下面的示例所示。
' Create a SalesOrderHeader query with two query paths,
' one that returns order items and a second that returns the
' billing and shipping addresses for each order.
Dim query As ObjectQuery(Of SalesOrderHeader) = context.SalesOrderHeaders.Include("SalesOrderDetails").Include("Address")
// Create a SalesOrderHeader query with two query paths,
// one that returns order items and a second that returns the
// billing and shipping addresses for each order.
ObjectQuery<SalesOrderHeader> query =
context.SalesOrderHeaders.Include("SalesOrderDetails").Include("Address");
另请参见
任务
如何:执行返回实体类型对象的查询(实体框架)
如何:使用导航属性导航关系(实体框架)